A comet is a small body made of ice and dust that orbits the Sun. As the comet moves closer to the Sun, it warms up and produces a tail of gas pointing away from the Sun.
A comet consists a solid core consisting or rock, dust, ice, and frozen gases known as a nucleus. The nucleus is surrounded by a thin atmosphere, called a coma, made of water and dust. The coma (and also the tails) can become illuminated by the Sun as the comet moves into the inner atmosphere and closer to the Sun. When the comets are farther away from the Sun, they remain frozen and inactive, making them very difficult to observe. The tails of comets form as they get closer to the Sun. The radiation from the Sun vaporizes some of the comet’s material which forms a stream away from the comet. This stream points away from the Sun.
Comets have been observed for thousands of years. Some of the earliest recorded observations of comets were by Chinese astronomers. Edmond Halley used Isaac Newton's newly developed laws of gravitation and motion to correctly predict the reappearing of a comet. This comet was named after him gaining the name 1p/Halley. Halley’s comet is a comet that is visible from Earth every 74-79 years with the naked eye. It will next be visible from Earth in 2061. Halley’s comet has been associated with many major historical events including the Battle of Hastings in 1066. It appears in the Bayeux Tapestry as the first recorded picture of the comet.
The Rosetta mission, launched by ESA (European Space Agency) on March 2, 2004, was a robotic mission to 67P/Churyumov–Gerasimenko, the first attempt made to land on a comet. As part of the Rosetta mission, a lander named Philae landed on the surface in 2014, ten years after the mission was first launched, to analyze the comet's structure. The mission taught us that the water on comets is different than the water found on Earth; it contains a bigger percentage of heavy water. Heavy water is like regular water, but replaces the hydrogen atoms with deuterium, an isotope of hydrogen. This led scientists to believe that the water found on Earth probably didn’t come from comets like 67P. The lander also discovered some carbon-bearing organic compounds, some of which are important in the making of amino acids. Amino acids are a group of chemicals that are very important to life on Earth.